I noticed that the scanlines script-fu was not present anymore, so I cooked up a new one. This one is completely self-contained. Has a few enhancements to it, making it easier to work with. Thanks to Federico Mena Quintero for his work on the original "Erase Every Other Row" script-fu which served as part of my guide.
The script-fu will install in "<Image>/Script-Fu/Enhance".
As a simple experiment, I took the instructions in the tutorial on the GimpTalk forums and created a script-fu for making PS-style gradient maps. The steps to do it are pretty simple, but I added a few new options to it, such as flattening image and layer opacity.
Works quick and should also be simple enough to work in either 2.2 or 2.4 without any problems. I have built and tested this in 2.4.5. If it doesn't work in the older versions, let me know and I'll try to work out whatever bugs come up.
Oh, and the original tutorial this is based on can be found here: